Free Fall

If you overcome your fear and have a go on this exhibit, you may experience the FEAR RESPONSE as well as a short period of WEIGHTLESSNESS.

The fear response is a series of biological reactions. They prepare your body to escape or face up to a dangerous situation - real or imagined. Humans are able to override their fears and many people really enjoy the response. Ask anyone who is involved in extreme sports!

As you free fall, you are pulled towards Earth by GRAVITY. You still have weight but you feel weightless because only air is pushing up against you. If you free fall while standing on a set of bathroom scales, they would measure zero as you fall. You get the weightless feeling to some extent if a lift suddenly moves down quickly.

Aim High

When you hit the rubber pad with the hammer, ENERGY is transferred from the hammer to the striker so it can travel up the cable and ring the bells.

The hammer and the striker both have KINETIC ENERGY while they are moving. To increase your chance of ringing the bells, you need to give the hammer more kinetic energy. It then has more energy to transfer to the striker. The most effective way to increase the kinetic energy is by giving the hammer a big swing and an extra push as it goes downwards. You could use a heavier hammer, since kinetic energy increases with MASS, but the hammer may be difficult to swing.

GRAVITY and FRICTION gradually slow down the striker until it stops at its highest point and falls back down.

Cha Cha

The main arm and the char arm can each rotate. When they both rotate, the cars travel a path that makes a complicated pattern.

The thrill and excitement of sideshow rides comes from the speed and direction change of the ride. ACCELERATION is the word given to changing speed or direction. It refers to speeding up, slowing down or going round corners without changing speed. Slowing down is also called deceleration. If you accelerate quickly, your body feels a strong FORCE. This force makes rides exciting for many people.

The controls refer to the rotation speed compared to the ground. If the main arm and the chair arm speed are both set at 5, they each rotate at the same speed compared to the ground. Try it and you will see that the chairs are stationary compared to the main arm. They seem to travel in one large circle.

This shows RELATIVE MOTION - the motion of one object compared to another object.

Cover Up

To cover the large circle with the smaller circles, you have to overlap the small circles. The problem is that when you position the circles, gaps are often left!

The total AREA of the five small circles is almost twice the area of the large circle, so covering the large circle looks easy!

The big circle is 20 cm across, with an area of 314 cm².

Each small circle is 12.4 cm across, with an area of 121 cm².

The five circles together have a total area of 605 cm².

This exhibit is an actual sideshow game. Normally, you place the small circles one by one. You cannot slide or adjust the circles once you have placed them. You probably would not be successful - even if you knew how to do it. Try it yourself and see.

Crazy Clowns

The clowns are a traditional sideshow attraction. They usually move their heads regularly from side to side. Even then it is difficult to get the winning numbers because these numbers are in the centre!

As a clown moves its head form side to side, it seems to go at the same speed all the time. It is actually slowing down as it moves towards the edges. The head must stop momentarily before changing direction. This means it spends more time pointing towards the outer numbers, which don't win a valuable prize.

It is difficult to win, even if you can predict the movement of the head. The way you place the ball in the mouth could make it bounce around and take longer to come out of the tube.

Curve Ball

Does the ball travel in a straight line or curve around? Where do you need to throw the ball so the other person can catch it?

If you look from above, you will see that the ball travels in a straight line compared to the ground. If you are sitting in one of the rotating chairs, the ball seems to curve. This is an example of RELATIVE MOTION - the path the ball seems to take depends where you are looking from and whether you are moving. That is, it depends on your frame of reference.

The ball travels straight across from one person to the other, but the other person continues to move while the ball is in the air. To allow the other person to catch the ball, it needs to be thrown to the position they are moving to!

Fortune Teller

Most people want to know their destiny. All of the fortunes are fairly broad and vague so nearly everyone can relate to them. If you want to believe, you can find something in the fortune that is relevant and important to you.

In this case your fortune is selected purely by chance when you touch the sensor. There are sixteen possible fortunes. Each fortune has an equal chance of being selected - that is, one chance in sixteen or a PROBABILITY of 1/16.

Framed

Machines like this one were often found in sideshows. They worked by turning a handle to show a short movie.

A series of pictures or frames is shown one at a time. Your eyes send SIGNALS to your brain about each one. When pictures are seen quickly one after the other, your brain 'fills in' what happens in between and movement is perceived. This is called the PHI EFFECT or the phi phenomenon.

Movement seems smoother as the pictures are shown faster.

Try this exhibit to see how many frames per second you need for movement to appear smooth.

The frames in early movies were shown fast enough for movement to appear smooth, but the film 'flickered'. This is why early cinemas were called the 'flicks'. When the rate is fast enough, the flicker disappears. Today, most movies show 24 frames in every second of film. Each frame is shown twice so you see 48 separate pictures each second, for a flicker-free movie.

Freaky Facts

Customers once paid to enter 'freak' show tents and see people or animals with medical conditions, different appearance or unusual skills.

Sometimes, people would deliberately change the way they looked so that they could earn a living at freak shows. The 'Great Omi', also known as 'Zebra Man' had his whole body and face tattooed with dark zebra stripes in the 1930s.

Tom Leppard is a modern tattooed man. His eyelids have been tattooed so that when his eyes are closed, you see leopard's eyes.

Robert Wadlow tried to live as normally as possible, although poor health and the need for money forced him to briefly appear in a circus. During this time, he refused to be dressed in costume and wore a suit instead.

Hugo Zamoratte performs in modern circuses as a contortionist. Traditional sideshows included contortionists, sword swallowers and snake charmers.

Gone With the Wind

When you hit the rubber sheet, the VOLUME of the cannon becomes smaller and the PRESSURE inside rises. Air always moves to areas of lower pressure, so it moves out of the hole.

A VORTEX ring is formed when air is shot from the cannon. Air pushed through the hole is slowed by FRICTION. Air near the edges of the hole is slowed down more than air near the centre. The fast-moving air has a lower pressure than the slow-moving air. This is called the BERNOULLI EFFECT. The difference in pressure causes the air at the edge to curve inward and the air in the middle to curve outward. This forms the vortex ring.

This can only happen because air can be squashed. It is a compressible fluid.

Water forms a vortex when it goes down a plughole.

Guillotine

Traditionally, sideshows have had a scary section with ghost trains and haunted houses. Today, sideshow alleys have a wider range of more realistic 'scare devices' such as this one.

When you use our guillotine, you probably know that you will be safe. How well you convince yourself that you are safe will determine how much of a FEAR RESPONSE you get. The guillotine device feels frightening because it gives sensations similar to those you would expect in the real guillotine. Your brain gets the message that these things are really happening to you!

The guillotine was invented by a French physician, Joseph Guillotin, as a humane way of killing those sentenced to death. More than 3 000 people were executed by guillotine during the French revolution and crowds gathered to watch.

Head Spin

Your brain monitors the movement of your body in a number of ways. One way is through the movement of your head. Embedded in your skull as part of your ear are three tiny tubes joined together. Each tube is looped and lined up at right angles to the other two, like three different faces of a cube.

The tubes are filled with fluid. At the base of each tube is a small flap. As your head changes its position, initially the liquid stays put to start with, because of its INERTIA, and it pushes back on the flap. This sends a SIGNAL to the brain. The liquid in the tubes then starts to move with the head.

When your head stops spinning, the liquid keeps moving. You think you are still moving. At the same time, signals from your eyes tell your brain that you have stopped. These confusing signals make you feel DIZZY.

In It to Win It

The ball will probably bounce out of the bucket if your throw is flat and the ball is not spinning.

A ball that hits a flat surface bounces off at a similar angles in the opposite direction. A lob shot travels along a very curved path and can hit the bucket so that the ball is less likely to bounce out.

You have more chance of getting the ball to stay in the bucket if you spin the ball to change its bounce. A ball with BACKSPIN will bounce more upright but not as high as expected. This happens because the spin causes a FRICTION force which slows the ball down. A tennis shot played with backspin is called a dropshot. With a lot of backspin, a ball can even bounce back the way it came.

TOPSPIN (spinning away from you as it travels) on a ball makes it bounce very fast and lower than expected. In this case the friction force pushes the ball forwards.

You can learn more about spin in Rebound.

Make Tracks

As a roller coaster car is lifted to the first peak, ENERGY from the motor is converted to POTENTIAL ENERGY. This stored energy is then used for the rest of the ride. There is a continual change between potential energy which depends on the height, and KINETIC ENREGY - the energy of motion. Excitement comes from ACCELERATION - the faster you change speed or direction the more exciting it is! A steep slope and sharp corners produce large acceleration, more forces on your body and more excitement.

FRICTION causes some of the coaster's energy to be changed to sound and heat, otherwise you could coast all day!

Morphin' Mirrors

When light hits a mirror, it is reflected or 'bounces' off at a similar angle in the opposite direction. If the mirror is flat, this gives you an image where you look 'normal'.

If the mirror bends inwards (a CONCAVE mirror) you may look larger, smaller or even upside down. This is because the light is reflected inwards towards a central point (the FOCAL POINT). These mirrors are used by dentists and are found in car headlights and telescopes.

A mirror that bulges outwards (a CONVEX mirror) makes you look smaller. This is because the light is being reflected outwards. These mirrors may reduce the size of the image, but you can see a wider area. Side mirrors on cars and shop security mirrors are convex.

Piggy in the Middle

When we pick something up, we use our muscles to lift the MASS of the object against the pull of GRAVITY. We say the object has WEIGHT. The more mass it has, the heavier it is.

When you lift something, muscles and tendons change length. Nerve endings detect these lengths and SIGNALS are sent to the brain. This information is stored in a 'memory file' so it can be referred to later.

When you first pick up a pig, your brain tries to find a match in the memory files. If the signals are similar to when you lift a one kilogram bag of sugar, you would decide that the pig must have a mass of about one kilogram.

Most of use don't have many 'memory files' for comparing weights, so at first we find it difficult to judge how heavy the pig is. It is much easier to judge when you have something for comparison.

Pluck a Duck

Pluck a Duck is for younger children and adults to share. Catching ducks is a traditional sideshow game. Young children will find it a challenge as their hand-eye coordination is still in the early stages of development. The Wacky Wire exhibit is more challenging and requires similar, but more developed skills.

People have always been fascinated by the unusual and the amazing. In Pluck a Duck, you can look underneath the ducks to learn some strange facts. Sideshows were one place where you might have seen the performances, competitions and people described under the ducks.

These facts were verified by GUINNESS® WORLD RECORDS© LTD at the end of 1999.

Rebound

A ball hitting a flat surface from one direction, bounces off at a similar angle in the opposite direction.

If you throw the ball directly at the target in Rebound, it is likely to bounce straight back over the basket. Throwing the ball upward in a curved path will make the ball hit the backboard at a different angle. It is then more likely to bounce in the the basket, but it may bounce out again!

Spinning the ball makes it bounce lower and at a different angle, so it is more likely to stay in the basket. The backspin bounce is slow, so the ball doesn't bounce very high even though it bounces more upright. The topspin bounce is fast and low.

If you throw a curved a lob shot with backspin, the ball will bounce off the backboard with topspin, and is more likely to go into the basket.

Revolution

When you see the tent wall moving, your eyes SIGNAL your brain about moving walls. Normally, these same signals would mean that you were moving - not the tent. Your brain thinks that you are actually moving.

However, your brain is also getting signals form your muscles and ears indicating that you are still. The brain is receiving conflicting signals, and this makes you feel DIZY.

If you watch the floor of the tent, you will not get the same effect because your brain will know that you are not moving.

When you are stopped in traffic, you sometimes think that you are moving when the car next to you beings to move. As soon as you look away, your brain reasons that you are not moving.

Spun Out

The water and ducks stay still for a moment when you spin the doughnut. This is because they have INERTIA - they will not change speed or direction unless something pushes on them. Eventually, FRICTION provides enough push to get them moving.

When the water and ducks move, they tend to travel in a straight line due to inertia, unless pushed in a different direction. However, the walls push the water towards the centre, making it travel in a circle rather than flying off at a tangent. This push towards the centre is called CENTRIPETAL FORCE.

The water and the ducks fly outwards due to inertia. It seems as if there is a force pushing them outwards. We often call it centrifugal force, although it is not a real force.

The ducks stay on the surface of the water. When the surface of the water becomes vertical, the ducks are floating sideways.

Stacks of Fun

When a ball is moving it has KINETIC ENERGY. A ball with more MASS or speed has more kinetic energy. For the light ball to have enough energy to knock over the cans, it needs to be travelling VERY fast. Otherwise, it cannot apply enough FORCE.

To knock a can over, you need to move the can's CENTRE OF MASS until is is no longer directly above the base of the can.

In normal cans, the centre of mass is in the centre of the can.

If cans or bottles are weighted at the bottom, their centre of mass is lower down. You now have to tip the can further before it falls over. This needs more force from a heavier or faster ball!

Track Attack

Track Attack feels realistic because your body has the same sensations as it would in the real thing. Many different senses are involved. Your brain organises the SIGNALS form your senses into something it recognises - you think you are on the ride. If the signals from the various parts of your body don't match, then you may feel DIZZY.

Your eyes are the most important movement detectors. Your ears let you know when you change direction. Also in the inner ear is a region that tells you whether your head is upright or at an angle.

Detectors in your muscles and tendons respond to stretching and detectors in your skin respond to pressure These detectors are called PROPRIOCEPTORS and send signals to the brain to keep it informed about your position and movement. Your brain processes all of this information and makes your muscles work to maintain your upright position. It all helps to make the ride feel more real.

Wacky Wire

When the spiral turns forward, you only have to move the ring down and the spiral threads through the ring - this is not too difficult.

When the spiral is not turning it is more difficult. You need to move the ring down and around. This involves a lot of different muscles. Your eyes and your muscles send SIGNALS to the brain so that it knows what is happening. Your brain then sends signals to your muscles to adjust the position of the ring.

Muscle movement relies on signals from certain parts of the brain. The MOTOR CORTEX sends electrical signals to muscles via the cerebellum in the brain. The CEREBELLUM controls fine movement for more accurate control.

Practice makes perfect!

Exhibit Notes Glossary

Acceleration

In everyday language, the word acceleration is used as meaning speeding up. In physics language acceleration occurs whenever there is a change in the speed OR the direction of motion. This could mean speeding up or slowing down. It could also mean changing direction at constant speed. Acceleration is a measure of the rate at which the change is occurring.

Going round corners, or going round in circles (circular motion) involves continually changing direction, and so requires acceleration even if the speed is constant.

For acceleration to occur, there must be a force causing it.

Acceleration is measured in metres per second per second (m/s² or m.s^-2)

Adrenaline (epinephrine)

Adrenaline is a chemical substance or hormone produced by the medulla (inside section) of the adrenal glands These glands are situated on the upper side of the kidneys. The adrenal medulla consists of a mass of nerve cells, and responds directly to stimulation by the nervous system.

The nervous system affects organs directly to elicit the fear response, but the effect is short lived. The adrenaline and noradrenaline that are produced in response to nervous stimulation provide an effect which lasts five to ten times as long.

Adrenaline is sometimes referred to as the fight or flight hormone. It forms part of a set of responses (in conjunction with the sympathetic nervous system) that prepares the body for extreme physical exertion. The set of responses is also known as the fear response or the General Adaptation syndrome, and it is designed to enable us to survive short term emergencies. The fear response was vital in our primitive ancestors for whom the response may have meant survival. It is initiated in the brain.

Noradrenaline (which is also produced by the adrenal medulla) has similar effects to adrenaline, except it has a lower effect on cardiac activity and causes greater constriction of blood vessels. Overall, noradrenaline increases peripheral resistance to blood flow, which in turn elevates blood pressure more than adrenaline.

Angular momentum

Momentum is a measure of ‘inertia in motion’. Greater inertia or higher speed means more momentum. (momentum = mass × velocity)

Angular momentum is the momentum of a rotating body and depends on rotational inertia and rotational speed (angular momentum = rotational inertia × rotational speed).

If no outside forces act on a rotating object, then angular momentum remains constant (is conserved). If the mass distribution in the rotating object changes, the rotational inertia changes. The speed of rotation then changes in order that the angular momentum remains the same.

The classic examples are ice skaters, divers or gymnasts who control their speed of rotation by changing their body position. The closer to the centre that the mass is, the faster they rotate.

Antinode

An antinode is a region of maximum vibration in a standing wave. A standing wave is set up when two waves of equal amplitude and wavelength pass through each other in opposite directions. The two waves together form regions of very large amplitude (the antinodes) and regions of zero amplitude (the nodes). Organs have pipes of lengths appropriate for standing waves to be produced to play a particular note.

Area

The size that a surface takes up is called the area. The surface may be curved like a ball or flat like a floor. There are different mathematical formulae used to calculate the area of different shapes.

The area of a square or rectangle may be calculated by multiplying the breadth and the height of two sides.

A circle’s area is calculated by πr², where π is approximately 3.14 and r is the radius (from the centre of the circle to the circumference).

Backspin

A ball in flight is said to possess backspin if the bottom of the ball is spinning away from you as it travels. To find out more, see ballspin.

Balance/Centre of Mass

An object is balanced if it ‘stays put’. It is said to be in equilibrium. There are a number of forces acting on the object, but the forces are balanced; they cancel one another out.

If the centre of mass of an object is directly above the base of the object, then it will not fall over. An object whose centre of mass is as low as possible is in stable equilibrium. You have to do work on it to make it fall over. If the centre of mass is well below the point of support, even better! An object whose centre of mass is at its highest is in unstable equilibrium and a small push (even a gust of air) could cause it to fall over.

An object such as a book can be in stable equilibrium when lying flat on a table, and also if standing upright. However it is far more stable when lying flat because its centre of mass is lower and it takes more work to make it fall over.

Balance in people

Balance is maintained through a number of mechanisms which normally work in harmony to keep us informed about our position and any changes to our position. The brain can then send messages to muscles to counteract any change in position in order to maintain balance. Once we have learned to walk, this happens automatically.

The main organ of balance is within the inner ear, but this is supplemented by information from our eyes, the degree of contraction of muscles supporting us, and pressure in the soles of the feet.

Within the inner ear, embedded in the skull are three cavities and the semicircular canals that contain fluid called endolymph and sensory hairs. When the head moves, the fluid moves, bends the sensory hairs and triggers a message to the brain. The three canals are at right angles to one another; one is vertical, and most sensitive to up and down motion, one is horizontal and most sensitive to side to side motion, and the other one is sensitive to tilting. The three work together to inform the brain about different types of motion.

When motion stops, the fluid continues moving due to inertia. The sensory hairs remain bent, and continue to send messages to the brain indicating motion. The other motion detectors, such as the eyes sense that motion has stopped and send conflicting messages to the brain. The result is a dizzy feeling.

Two other cavities within the skull, the saccule and utriculus have hair receptors covered with a jelly like membrane. Embedded in the membrane are chalky granules (crystals of calcium carbonate) called otoliths. If you change speed or if your head tilts, the inertia of the otoliths cause the hairs to bend and signals are sent to the brain to inform it what has happened.

When you spin, your eye muscles work hard. They stay focused on one object as your body moves round, then quickly move to focus on another object as the first one goes out of view. The eyes act to ‘stop the world from turning’. People who twirl round a great deal are like ballerinas, use rapid head movements to enable them to focus their eyes on stationary objects for more extended periods. Through training, they are also able to take more notice of the brain messages coming from the eyes, and less from the semicircular canals. That way they can continue to spin without feeling the effects!

Ball spin

A ball follows a curved path as it travels through the air. It continues to travel horizontal with (close to) constant velocity, and at the same time it accelerates downwards due to gravity. This is projectile motion. In the absence of air the path is a parabola.

If a ball spins as it travels through the air, it follows a path that is more curved than the path caused by acceleration due to gravity (projectile motion).

This extra curve is explained by Bernoulli’s Principle.

Topspin on a ball means that the top of the ball is travelling along the path of the ball and also travelling forwards due to its spin. The bottom of the ball is travelling forwards along the path of the ball, but spinning in a direction opposite to the direction of the ball’s travel.

The effects of spin depend in the main on the layer of air which surrounds and ‘clings to’ the ball. This layer is called the boundary layer. At the top of the ball the boundary layer is moving round with the ball and is being hit by the air the ball is travelling in. The air molecules collide and build up producing a high pressure. At the bottom of the ball, the boundary air is moving away from the air molecules the ball is bumping in to. Molecules collide less and a low pressure results. The high pressure above the ball and lower pressure below causes the ball to be pushed downwards as it travels.

Conversely, a ball with backspin will tend to rise as it travels. A ball can also be spun ‘sideways’ and so curve laterally as it travels through the air.

The amount of curve on a ball as it travels depends on its speed, its rate of spin, its mass and the surface structure. The maximum curve is obtained with a ball with slow speed, fast spin, low mass and large rough surface.

Ball spin also affects the way a ball bounces.

Bernoulli’s principle

When air (or any fluid) flows smoothly, its pressure decreases as its speed increases.

Bouncing

This is the springing back of an object that hits a surface. In the context of the sideshow exhibition, the objects that bounce are balls. When a hard round ball bounces on a smooth surface, it bounces off in the opposite direction, but at the same angle at which it arrived.

A ball with spin bounces off at an unexpected angle. A ball with topspin dips as it travels through the air. It bounces from a surface much faster and with a lower angle. A ball with bottom spin rises as it travels, and it moves slower after bouncing and at a higher angle than expected. Balls with sidespin will rebound sideways off the surface, and are often used by cricketers!

How high something rebounds when dropped depends on the height it was dropped from, the material the ball is made of, and the material in the surface it bounces off. A ball cannot rebound to a point higher than the point it was released from. To do that would require an input of energy, since energy cannot be created nor destroyed, it can only be converted from one form to another. As the ball falls, potential energy is converted to kinetic energy. When contact is made with a surface, the kinetic energy is quickly converted into other forms of energy. Some energy is stored in the ball as it is squashed out of shape, some is transferred from the ball into heat and sound. If a ball bounces back to a height that is close to the position it was released from, then little energy was lost during the collision between the ball and the surface.

A collision between two objects where there is no loss of kinetic energy or momentum is termed an elastic collision. It seems likely that this type of collision is only possible at the atomic level.

Centre of mass

An object’s centre of mass is the point where its average mass lies — the average position of the total mass of an object. An object will balance if supported at a point directly underneath the centre of mass.

Centre of gravity is another term often used for this. Here on Earth, for the objects that we will consider, either term can be used.

Centripetal force

See Circular motion.

Cerebellum

The cerebellum (found at the base to the rear of the brain) is responsible for balance and muscular coordination. It plans motor activities and monitors and correctively adjusts signals from other parts of the brain — it does the fine tuning in response to feedback. It also enables the eyes to move smoothly as they track a moving object.

The cerebellum also uses past experience to keep a record of movements and their timing. As you repeat a series of movements in sequence, the memory gets filed, so that you can later repeat the sequence easily. A case of practice makes perfect!

Chance

Chance is the likelihood that something will happen. It is the same as probability but is usually associated with unpredictable events or luck.

Circular motion — centripetal force

All moving objects naturally travel in a straight line. To make an object deviate from the straight line a force is needed. To go round in circles, there must be continual change in direction, which requires continual force. The force must always be pushing/pulling the object in towards the centre of the circle. This force is called centripetal force. (Centripetal means ‘centre seeking’).

An object can be whirled around your head on a piece of string. If you let go of the string, you remove the centripetal force and the object then goes in a straight line — it flies off at a tangent. This is demonstrated in sporting events such as discus and hammer throw.

Collisions

Collisions are regular occurrences in everyday life — a tennis racquet hits a ball, a hammer hits a nail, two cars try to occupy the same section of road, a chemical reaction occurs because atoms collide. In all of these there are forces involved and exchange of energy between the components of the collision.

Collisions are usually categorised as elastic where the objects involved return to their original shape after the collision, and inelastic, where the objects become permanently distorted or fused together. In both cases momentum is conserved. Mechanical energy is conserved in elastic collisions, but in inelastic collisions some of the mechanical energy is converted to other forms of energy and so is not conserved.

Concave

A concave mirror is part of a mirrored sphere, used so that it seems to cave in when viewed. It reflects parallel rays of light towards a point called the focal point. Objects reflected by a concave mirror appear larger, smaller, upright or upside-down, depending on the location of the focal point of the mirror.

Consonance

Consonance is achieved if two notes played together produce a pleasing sound; the two notes are said to be consonant. Two notes that produce a harsh or unpleasant sound when played together are said to be dissonant.

Convex

A convex mirror is part of a mirrored sphere, used so that the mirrored surface bulges outwards towards the viewer. It reflects parallel rays of light outwards as if coming from a point (the focal point) behind the mirror. Objects observed with a convex mirror appear small, but a wider area can be seen.

Co-ordination of movement

Movement requires contraction and relaxation of muscles in response to electric signals from the motor cortex of the brain. The left side of the brain controls the right side of the body and vice versa. Control of movement for accuracy or very small movements involves another region of the brain, the cerebellum. This controls the contraction and relaxation of each muscle so that movement is smooth and not jerky. The cerebellum helps plan the motor activities. It also receives signals from the eyes and feedback from your arms and legs about where they are placed and makes corrective muscle adjustments. The cerebellum also enables the eyes to move smoothly as they track a moving object. A structure in the mid brain — the substantia nigra also acts to promote smooth voluntary body movements, producing the grace of practised movements in gymnasts, ballet dancers, and trapeze artists.

Cortisol is a chemical (a steroid) produced in response to danger. It is produced by the outside region of the adrenal glands (adrenal cortex) and acts to raise the blood sugar level by stimulating the liver to initiate the process of glucose production from fat and protein. It also acts as an anti-inflammatory. (Hence its therapeutic applications as cortisone). Cortisol is found in high quantities in persons suffering from stress.

Dizzy

Dizziness is a state produced when conflicting messages are sent to the brain concerning the motion of the body, you say you feel dizzy.

If you spin around and then stop, the fluid in the semicircular canals (see Balance) continues to move due to inertia, and so messages are sent to the brain indicating that you are still spinning — even though you have stopped. The brain then receives ‘spinning’ messages from the ears, but ‘stationary’ messages from other parts of the body. The conflicting messages cause dizziness.

Trying to walk in a straight line immediately after stopping spinning can cause you to fall over. The muscles of your body automatically contract to counteract the spinning but the spinning isn’t happening any more. If you spin round to the left and stop, walking in a straight line is usually a walk/fall to the right. Even if you stand still the world seems to be spinning. The brain is sending messages to the eyes to keep moving to counteract the spinning!

If the feelings of dizziness do not result from motion, then the condition is called vertigo.

Dopamine

This is one of a number of neurotransmitters. Dopamine is involved in emotional behaviour as a ‘reward chemical’. It probably evolved as an internal reward for making choices that were survival enhancing. It is the chemical that makes pleasurable experiences pleasurable. (Recent research suggests that all addictions are based on the ‘pleasure’ associated with the dopamine increase initiated by particular chemicals — this includes addiction to alcohol, nicotine, cocaine and chocolate).

Dopamine also strongly affects learning and memory, and muscle control. Lack of dopamine has been linked to Parkinson’s disease in which muscular control is progressively lost, and uncontrollable shaking results. High levels of dopamine have been linked to schizophrenia and the mood swings associated with that disease (as well as the mood swings associated with addiction).

Endorphin

A name derived from endogenous morphine. Chemicals called endorphines are pain relieving chemicals very similar in structure to the opiates (the pain killers derived from the opium poppy — including morphine, codeine and heroin). They are produced in response to fear or stress — probably to enable fight or flight regardless of injury. They also induce a state of euphoria.

Energy

Energy exists in many different forms. We are very familiar with heat, light and electrical energy. When anything happens, energy in one form is changed to a different form of energy. Energy is never lost, it just gets changed from one form to another. Anything that has energy is capable of doing work.

Potential energy is often called stored energy.

Gravitational potential energy is the energy something has because of its position compared to another (usually an object with much greater mass). It is commonly used to refer to the amount of energy something has because it is under the influence of Earth’s gravity.

For example an object two metres above the surface of the earth has twice as much gravitational potential energy as an object one metre above the surface.

An object held in a gravitational field will start to accelerate as soon as it is released, and it can then do work as it falls and/or lands.

Kinetic energy is the energy that something has just because of its motion.

The more mass something has, the greater its kinetic energy when it moves. The faster it moves, the greater its kinetic energy.

The quantity of kinetic energy is given by K.E. = ¹/₂mv². The mass (m) is the mass of the object, the velocity (v) is a measure of the speed of the object. Since the energy depends on the squared value of the velocity, a small increase in velocity can have a marked impact on the energy.

As something falls in a gravitational field, its potential energy is converted continually to kinetic energy. Immediately before impact, the kinetic energy is a maximum and the potential energy has reduced to zero.

When a moving object collides with something and is stopped, its kinetic energy is converted to other forms of energy, usually heat and sound.

Kinetic Energy (and all other forms of energy) is measured in joules (J).

Ellipse

An oval shape made by stretching or squashing a circle. The shape is shown by the cut edge formed when a cone is standing on its base and is cut right across. (So it is officially a plane curve belonging to the conic family.)

The flatter the ellipse is the more eccentric it is said to be. A circle can be considered to be an ellipse with an eccentricity of zero. An ellipse that is close to a straight line has an eccentricity close to one.

Enteric nervous system

The enteric nervous system is a complex network of millions of nerves linked to the oesophagus, stomach and intestines are a relic of our far distant ancestors. It was very important millions of years ago when the most important survival behaviours were finding food and avoiding becoming food.

The enteric nervous system has been called the brain of the intestinal system because it is complex, can transmit nervous impulses and process information, and is present in all vertebrates. It also produces and responds to the same chemicals as the brain, including dopamine, which is associated with pleasure, emotions and addiction. The brain and the enteric nervous system both form from a structure called the neural crest. This appears and divides in the foetal stage, and the two structures remain linked.

Normally the enteric nervous system controls the muscles of the gut, and we are totally unaware of its actions. In times of sudden stress, signals from the brain reach the enteric system via the vagus nerve. The actions of the enteric nervous system result in the ‘queasy feeling’ in the stomach that signals fear. It can be accompanied by stomach cramps, diarrhoea, or vomiting. Different people respond in different ways to this signal at different strengths, hence the variety of physical indications of its action. The main aim is to prepare the body for ‘fight or flight’ — easier on an empty stomach! The enteric nervous system also triggers the immune system by causing special cells (mast cells) in the lining of the small intestine to produce a range of inflammatory chemicals including histamine.

The hormone adrenaline works alongside the enteric nervous system.

Epicycloid

This is the name given to the path traced by a point on the outside of a circle when it rolls around another circle. Arches are formed around the fixed circle. The number of arches depends on the ratios of the fixed and rolling circles, and is determined by the equation

number of arches = radius of rolling circle ÷ radius of fixed circle

Fear

Fear is a complex emotional feeling! Signals of potential or imagined danger are received by the brain and the fear response is triggered. The brain stimulates the enteric nervous system and triggers the adrenal glands to produce adrenaline and cortisol. Together these bring about a number of physiological responses called the fear response, that prepares the body to take immediate and vigorous action — by fighting or fleeing.

When a particular stimulus invokes unreasonable fear of objects or situations, and action is taken to avoid that stimulus, then a person is said to have a phobia.

Fear Response

A number of responses that together prepare the body to take immediate and vigorous action — by fighting or fleeing.

When in a frightening situation, there is great increase in the activity deep in the brain — in the mid brain, particularly the amygdala (a-mig-da-la) region. The amygdala region evaluates the situation and initiates the fear response if deemed appropriate. (Interestingly, the amygdala connects to the olfactory (smell) system, which may explain the ‘smell of fear’)

The adrenal medulla responds to direct nervous stimulation to produce adrenaline, and the enteric nervous system activates.

Nerves from the amygdala link to another small structure of the brain — the hypothalamus. The hypothalamus regulates emotions and when stimulated induces feelings of pleasure. The hypothalamus then produces a hormone that integrates and regulates the fear response, and activates the pituitary gland. In response to signals from the pituitary gland, the adrenal cortex produces cortisol. This chemical is often measured as an indicator of stress levels.

Signals are also sent to another area of the brain, the hippocampus, which enables formation of memories of the incident. It probably also recalls memories of previous similar situations for comparison.

A range of physiological responses are brought about through the actions of the enteric nervous system, and the hormone adrenaline. Heart activity increases, increasing blood supply to the brain and muscles (hence the pounding heart). Blood flow is channelled away from the skin and the intestines (hence the white skin and queasy tummy), again providing brain and muscles with more blood. Breathing becomes faster and deeper and saliva and mucous dry up (hence the dry mouth). This increases the rate of gas exchange in the lungs, and keeps the blood well saturated with oxygen. Blood sugar level is raised and muscles tense to prepare the body for rapid and vigorous action. The pupils dilate, making the eyes more sensitive, and the hairs stand on en, possibly a remnant from the days when our ancestors were more hairy and fluffed up hair made them look larger and more scary. Perspiration increases to keep the body cool as it fights or flees, and more white corpuscles are produced to fight infection — just in case!

A feeling of exhilaration accompanies the fear response when action is taken. This is a ‘high’ which can become addictive (hence the adrenaline junkies who deliberately jump out of perfectly good aeroplanes, or off bridges when tied on by a piece of elastic). The fear response lasts for an extended period of time.

The body does not differentiate well between short term emergencies (fear induced) and long term anxieties, and it responds to both in a very similar way. The amygdala is involved in both, although processing may occur in different parts of the amygdala. Stress and its associated diseases are the result.

Focal Point

For a spherical concave or convex mirror, the focal point is at the centre of the sphere that forms the curve of the mirror. If parallel light rays are reflected from a mirror, the light passes through, or appears to come from the focal point. (See concave and convex mirrors).

Force

The science name for a push or a pull. Forces are due to the interaction between two objects, and they tend to cause a change in speed, direction or shape.

Forces are always applied when two objects come into contact. Some forces act at a distance with no contact necessary oe for example gravitational force.

If all the forces acting on an object balance one another out, there will be no net force or overall effect. The object will be in balance (in equilibrium).

Force is measured in newtons (N).

Frame of reference

All motion is relative, or measured in respect to something else - it depends where the motion is observed and measured from.

If you are sitting still reading these notes, than you may say that you are not moving. Relative to the Earth, with the Earth as your frame of reference you are indeed stationary, but the Earth is spinning on its axis and travelling in orbit around the Sun. If the Sun was your frame of reference, you would be far from stationary.

Free Fall

If something is moving under the influence of gravity alone, it is said to be in free fall. Galileo investigated free fall (possibly by dropping a whole range of things from the leaning Tower of Pisa), and determined that in the absence of air resistance, all objects free fall at the same rate regardless of their mass. They are accelerated towards the centre of the Earth by a force we call gravity.

Frequency

Frequency is a measure of how often an event is repeated.

Sound is produced only when a medium vibrates. In the study of sound, frequency refers to the number of vibrations in a second and is given the unit of hertz (Hz). In physics, the note of middle C has a frequency of 256 Hz.

Friction

Friction is a force that tends to prevent one surface from sliding over another. It is not fully understood, but we do know that it varies with pressure and speed of movement, and it may be reduced by covering surfaces with a lubricant that separates the two layers.

All surfaces are bumpy. Even a very smooth surface has very tiny bumps.

When two surfaces are together, the bumps provide the points of contact. The contact area is small, so pressure is very high and strong attractive forces bind the molecules of the two surfaces together. A force is needed to overcome these binding forces and the force of friction. If pressure on the surfaces is increased, then there is more binding, and so friction is greater.

Gravity/gravitational forces

‘Gravity keeps your feet on the ground.’ Any two objects are attracted to one another. The force that exists between them is called a gravitational force. If the force was strong enough, then it should cause the objects to accelerate towards one another. You don’t usually see objects crashing towards one another because the attractive force is quite small, and friction prevents the objects from moving. On Earth, the force between them is also VERY much smaller than the force attracting them to Earth. A 60 kg person is attracted to a nearby 60 kg person with about 40 billionths as much force as they are attracted to the Earth.

The more mass each object has, the greater is the attractive force. When one of the objects is as massive as the Earth, then the attractive force becomes more obvious.

When you drop a ball you see the ball falling towards the Earth. What you don’t see so easily is the Earth rushing up to meet the ball.

Both the ball and the earth have the same force acting on them, and they accelerate towards one another. The Earth is so massive that it has great inertia and the force only causes a small acceleration! The Earth doesn’t travel very far before it collides with the ball. The ball meanwhile has travelled a greater (and therefore more obvious) distance — the force was sufficient to accelerate its much smaller mass significantly.

The value of the gravitational force between two objects depends directly on the mass of the objects and inversely on the square of the distance between the objects.

The equation is F = Gm₁m₂ ÷ d²

So double the mass of one of the objects and the gravitational force each object experiences is doubled. Double the distance between the two objects and the gravitational force each object experiences is decreased by a factor of two squared. (ie it becomes one quarter of what it was.) This explains why we don't get sucked off the Earth by the Sun, which is so much more massive than the Earth.

The gravitational field close to the surface of the Earth is sufficient to cause objects to accelerate downwards at a rate of approximately 9.8 metres per second per second (9.8 m/s²⁾. Which means that every second its downwards speed increases by 9.8 metres per second. You might think that objects with more mass should have a greater acceleration and therefore fall quicker. Not so, in the absence of air resistance, all objects close to the Earth’s surface accelerate towards the centre of the Earth at the same rate. An object with more mass causes a greater gravitational attraction, but it has more inertia so it is more difficult to change its motion. These two balance out.

The normal force due to Earth’s gravity causes an acceleration of about 9.8 m/s ². It is sometimes referred to as a g force. A force that causes an acceleration of twice this (ie 19.6 m/s²), is called a 2g force (pulling 2g as they say in popular movies such as Top Gun!)

Hormone

Hormones are often termed the chemical messengers of the body. The name hormone comes from hormon meaning to stir up. They cause a response when they reach their target organ(s).

The system of hormone producing glands is called the endocrine system, from endon meaning within and kinein meaning to separate. Hormones are produced within glands, and are released into the blood stream. Each hormone causes particular responses in particular target cells. This system is slower than the nervous system. Nerve impulses travel very quickly directly to the target, whereas hormones are carried in the blood, which is a less direct and much slower system.

Hydraulics

Hydraulics refers to the use of pressure in liquids to produce a machine. A hydraulic machine works because liquids have pressure and are difficult to squash. A pipe filled with liquid has two cylinders, one at each end. In each cylinder is a piston. When the piston in the master cylinder at one end of the pipe is pushed inwards, pressure is transferred through the liquid, so the piston at the other end (in the slave cylinder) moves out.

A small force on the piston of the master cylinder can produce a large force on the piston of the slave cylinder, and so move a heavier load. This happens if the slave cylinder has larger diameter than the master cylinder. It is pressure that is transferred through the liquid, and pressure depends on force and area.

Pressure = Force ÷ Area

Pressure is constant!

So F/A for the master cylinder = F/A for the slave cylinder

Small force/small area = large force/large area.

The brake system of a car uses hydraulics. When the brake pedal is depressed, the force on the piston creates pressure which is transferred through the brake fluid. The piston at the other end pushes out and pushes the brake pads or discs so that friction can slow the car down. If air gets into the system the brakes do not work as well because the air compresses.

Inertia

Objects resist any change in their movement. Inertia is the name given to this resistance. An object will not change what it is doing unless a force causes it to change. So a stationary object will stay put unless it is pulled or pushed. In fact it would seem quite strange if that was not the case!

A moving object will continue to move in exactly the same direction, and at the same speed unless it is pulled or pushed. This does not seem so obvious in everyday life. Many objects that are moving (like cars) seem to need continual pushes to keep them going. That is because there are unseen forces slowing them down. We call the unseen forces friction. Friction between the car and the air it is travelling through is also termed drag. Car designers try to reduce drag by making cars a streamlined shape. At high speeds drag can have a significant impact on the speed of a car.

Inertia is measured in kilograms (kg).

Kinetic energy

(see Energy)

Mass

Mass is a measure of the amount of inertia that something has, or a measure of the amount of stuff that something contains. It is a constant for the object and does not depend on where the object is or what is happening to it. Compare this with weight, which is the force an object experiences because of gravity.

Mass is measured in kilograms (kg).

Memory

Memory involves the processing of information in three successive stages:

1. Sensory memory which stores exact copies of sensations very briefly, at the most a few seconds, and in the case of visual input, for only a fraction of a second. This allows information to be held long enough to move it on for further processing.
2. Short term memory which stores information for about 20 seconds. The information is then lost unless it is practised and transferred to...
3. Long term memory where it can be stored indefinitely. To recall this information, it is necessary to bring it out of long term memory back into short term memory for use.

Momentum

Momentum is inertia in motion. It is calculated as the product of mass and velocity; ρ = mv.

A force must be applied to an object to change its momentum. In rugby league a hard tackle is needed to change the momentum of a speeding winger or a not quite so speeding forward.

Momentum is measured in newton-seconds (Ns).

Motion sickness

Motion sickness occurs when several different senses send conflicting messages to the brain about the position and motion of the body.

It is caused in the same way as dizziness, but can literally result in nausea and vomiting.

Motor cortex

The cortex is an outer layer of the brain, deeply folded to allow a larger surface area and more nerve cells.

The motor cortex consciously controls voluntary muscular movements. Certain body areas such as the hands and mouth have proportionately greater areas of the cortex devoted to them. The greater number of nerve cells controlling a region means that there can be very fine control of movements.

The motor cortex usually works in conjunction with the sensory cortex and cerebellum to control muscle activity.

Myelin

Nerve cells or neurones conduct electrochemical signals along to another nerve, or effector organ (muscles or glands). Sometimes, the nerve can be up to one metre long and needs to be an efficient conductor of the signal. Myelin sheaths are often laid down to ‘insulate’ parts of nerve cells (the axon fibre) and ensure the signal is conducted well. Often, the myelin sheath is thicker than the axon fibre itself.

Myelin is made from a fatty substance (a lipid sphingomyelin used in cell membranes) and is produced by Schwann cells. These cells envelop and rotate around the nerve axon, leaving multiple layers of myelin. White matter in the brain is the myelinated part of nerve cells, while grey matter is the unmyelinated nerve cell sections.

Degeneration of the myelin sheath lowers the efficiency of electrochemical transmission along nerve cells. This reduces muscular control, causing spasms and loss of fine motor control. It is currently believed that degeneration may happen due to the body’s immune system attacking the myelin sheath.

Neurotransmitter

A neurotransmitter is a chemical substance produced and released by a nerve cell (a neurone). It generally transmits the nerve signal across the gap (synapse) from this nerve cell to another. For the signal to begin in the next nerve cell, there needs to be sufficient quantity of neurotransmitter produced.

Nerve endings, or receptors

These are specialised structures in sensory neurones. The receptors are sensitive to temperature, touch, sight, sound, taste or chemicals (smell), and once activated, a signal is transmitted to the brain by nerves.

Node

A node is a region of minimum vibration in a standing wave.

A standing wave is set up when two waves of equal amplitude and wavelength pass through each other in opposite directions. The two waves together form regions of very large amplitude (the antinodes) and regions of zero amplitude (the nodes). Organs have pipes of lengths appropriate for standing waves to be produced to play a particular note.

Normal

When studying reflection, it helps to draw in a line perpendicular to the reflecting surface at the point where the reflection occurs. This line is called the normal, and is the line from which angles are measured. The angle between the approach path and the normal is called the angle of incidence. The angle from the reflected path to the normal is called the angle of reflection.

When considering reflection of light and sound, the angle of incidence is equal to the angle of reflection. With ball bounces, the reflected path angle depends on the forward velocity of the ball, the smoothness of the reflective surface and the degree of spin on the ball. (See ballspin).

Peer group pressure

Peer group pressure causes many people to make decisions to do things despite their better judgement, usually to try to impress and gain greater acceptance by a group. As we mature we are less susceptible to peer group pressure, but it is still evident. Young adolescent males are particularly prone to applying and responding to peer group pressure. It is important that people are given the chance and encouragement to make their own decision about what is best for them.

Phi effect (Phi phenomenon)

The perception of motion as a result of seeing a number of separate, slightly different pictures in quick succession is due to the phi effect. The brain receives information about the individual images and infers what happens in between. Movement is perceived. It is an interpretation capability of the brain (ie primarily psychological rather than primarily physiological) called the phi effect or the phi phenomenon. It is this effect that enable us to watch the movies (moving pictures) and interpret smooth motion!

The phi effect is enabled by your visual sensory memory your so called iconic memory, which stores exact replicas (icons) of. The iconic memory retains memory for only a fraction of a second before passing information on to the short term memory. Movie films are projected so that each successive frame appears just before the previous one left the iconic memory. This makes successive images blend together and create the impression of smooth movement.

Movement appears smooth if sequential images are projected at least 24 times per second. For some people the effect needs only 20 times a second, but at a rate lower than this, movement appears jerky.

Movement perception for many years was thought to be due to persistence of vision, but this idea has been superseded.

Pi (π)

Pi is a constant that relates to circles.

It is the ratio of the circumference to the diameter of any circle.

π = c ÷ d

Pi is an irrational number (ie it cannot be expressed as a fraction or written in exact form as a finite decimal). Its approximate value is 22/7 or 3.142.

The value is used in calculating lengths areas and volumes of circular figures and solids.

Pitch

This is the term used to indicate the high or low a sound is. Sound is generated when an object vibrates and leads to vibration of the air around it. A sound wave can be set up if the object is moving at the right frequency (20 to 20 000 vibrations per second (Hz)). If the frequency of the sound wave is high then the sound will have a high pitch. On the other hand, low pitched sounds result from slower vibrations.

Potential energy

(see Energy)

Pressure

Pressure is a measure of how much force there is on each bit of a surface; the force per unit area and is calculated using the equation:

P = F ÷ A

More pressure results from a person wearing stilleto heeled shoes than a person wearing sneakers because the same weight is ‘concentrated’ into a smaller area. (In fact a person standing on the heels of their stilletos produces greater pressure than an elephant in bare feet.)

Pressure is measured in pascals (Pa).

Probability

Probability is an indication of how likely it is that something will occur. It has a value between zero (it definitely won’t happen) and one (it definitely will happen). Often the values are expressed as percentages, so a probability of one has a 100% chance of occurring.

Mathematics can be easily applied to determine probability, usually based on the idea that there is an equal opportunity for each of the possible happenings. For example when using a ‘fair die’, over a large number of throws, each number on the die comes up the same number of times.

Where several equally likely outcomes are possible, the probability of an event can be calculated by:

Number of events favourable to the outcome ÷ Total number of possible events

The probability of a coin landing on heads after being flipped is 0.5 or 50%.

No matter what the history of a coin, each and every time it is flipped it has a 50% probability of landing on heads.

Projectile motion

Any object that has been thrown or propelled but no longer has any contact force on it is called a projectile.

Once released, its path is determined by its initial speed and direction, by the effects of gravity, and by the effect of air. The faster it is going to start with the further it will travel before it hits the ground. In the absence of air, the path taken is a parabola. This is the path because the projectile continues to travel with constant horizontal speed, while at the same time accelerating towards the earth due to gravity.

In air the path is very close to a parabola unless the projectile has spin or air resistance is high (for high speed projectiles) in which case the projectile does not travel as far before it hits the ground.

The projectiles in this exhibition are primarily balls. If a ball moves really quickly through the air then a turbulent flow of air occurs behind the ball as it moves. The turbulence causes the ball to slow down, as the ball loses energy in creating this turbulence. The faster the ball, the greater the turbulence and the greater the slowing down. This does not apply in this exhibition, since balls will generally be travelling slowly.

A thin layer of air called the boundary layer clings to the ball. If the surface of the ball is rough, the boundary layer clings to the ball better, reduces the turbulence behind the ball, and reduces the amount of slowing down that the ball experiences. The ball travels faster, and therefore further, like golf balls with dimples.

Proprioreceptors

Nerve endings that respond to muscle and tendon stretch are called proprioceptors. They send signals to the brain, giving it information about the location of each part of the body.

Random

A sample taken from a group of objects is said to be random if every object has an equal chance of being chosen. Similarly, a random event is one that has an equal chance of occurring as any other event.

Receptors

See nerve endings.

Reflection

Literally ‘bouncing’, this is the process that occurs when objects or radiation travelling in one substance collide with a different substance and do not enter the second substance, but bounce from the surface. The law of reflection states that the angle of incidence is equal to the angle of reflection, and this law holds generally true for reflection of light. Reflection of balls from surfaces is affected by the ball spin also.

Reflection of light from curved surfaces (mirrors) still follows the law of reflection and therefore can result in ‘distorted images’.

Reflection from plane (flat) mirrors

The process can best be described by a ray diagram which selectively shows the path of few rays of light to indicate the formation of an image.

Some rays of light from an object hit the mirror and are reflected back into the eyes of the observer. These initiate signals to the brain which then interprets the rays of light as coming directly from an object.

In the case of a plane mirror, the image seen is virtual: the rays of light reaching the eye are those that would come from an object as far behind the mirror as the actual object is in front of the mirror. Our brain interprets the rays of light reaching the eye as the object behind the mirror, even though it is not really there. (The simplest form of virtual reality).

Reflection from curved surfaces

Reflection of light obeys the laws of reflection, the curving mirror causing images that are not a true ‘copy’ of the object!

There are two types of curved mirror: those that curve inwards, away from the observer (concave mirrors: they cave in), and those that curve outwards towards the observer (convex mirrors).

Concave mirrors can produce a variety of effects, depending on the degree of curvature of the mirror and the distance the object is from the mirror. A convex mirror always produces an image that is smaller and closer to the mirror than the real thing.

Relative motion

All motion is relative, or measured compared to something else. For example, if you are sitting still reading these notes, than you may say that you are not moving. Relative to the Earth you are indeed stationary, but the Earth is spinning on its axis and travelling in orbit around the Sun. Relative to the Sun you are far from stationary.

If two cars are travelling alongside one another, each travelling at 60 km/h according to the speedometers, it means that they are travelling at 60 km/h compared to the road (or relative to the road). However if a passenger in one car looks at the other car, it seems to be stationary its motion is zero relative to the observer.

If you are stationary at the traffic lights and the car next to you moves forward as you are looking at it, you sometimes get the feeling that you are moving backwards. Your motion is backwards relative to them.

If you walk down the aisle of a bus with its speedo recording 80 km/h, you may travel at 1 km/h relative to the bus, but 81 km/h (or 79 km/h) relative to the road. The speedo is of course recording the instantaneous speed of the bus relative to the road. This links in to frame of reference, in that it depends where the motion is observed and measured from.

Resonance

Resonance is the phenomenon of increased amplitude of vibrations due to forced vibrations that match the natural vibrations of an object. For example a child on a swing can make the swing go higher and higher (increase in amplitude) by forcing their legs to swing backwards and forwards (vibrate) at the correct frequency!

Resonance in strings or air columns leads to noises that can be tailored to produce music.

If you produce a sound that has the same frequency as the natural frequency of a glass. Then the glass will start to vibrate very strongly at that frequency. It will resonate. The vibrations can be so strong that the crystal structure of the glass can break.

Risk taking/thrill seeking

Some people live for thrills, others avoid them! Why do some people love bungee jumping, scary movies, fast cars and rock climbing? Its part of your personality. Frank Farley (psychologist) has studied risk taking behaviour. If your behaviour is guided by novelty and risk then you are a T-type person, but if you prefer the status quo and the quiet life, then you are a t-type person. T-types may need a higher level of physiological arousal than others, and they gain that by taking risks. Risk taking is not just physical risk, it can be mental or business risks. You could put Einstein and Alan Bond into the same category as risk takers. Farley believes that without T-types, there would be no human progress!

Stimulation of the fear response may accelerate the production of dopamine, a chemical linked to pleasure, emotions and addiction.

Rotational inertia

Sometimes called moment of inertia, rotational inertia is the tendency of a rotating (spinning on an axis) object to keep on rotating, or for a stationary object to resist rotation. A torque must be applied to bring about a change.

With inertia, mass was an important consideration. With rotational inertia, mass and the distribution of the mass are both important. The further the mass is from the centre of rotation, the greater the rotational inertia. A tightrope walker will often carry a long pole, preferably one that is heavy at the ends. The rotational inertia is then increased, so rotation (and falling off) is resisted!

Semicircular canals

See balance in people.

Sensory cortex

The brain has an area called the cerebrum with an deeply folded outer layer called the cortex. The folding allows a larger surface area for storing more nerve cells.

The cortex is responsible for voluntary body movements (motor cortex ) and receiving sensory information (sensory cortex) and storing certain memories.

When doing a particular activity, sensory signals (touch, sight, etc) are sent to the sensory cortex. ‘Memories’ of different motor movement patterns are then stored in the sensory cortex: these are sensory engrams of the motor movements (ie the movement has been learned).

For example, when learning to cut with scissors, a child will learn how to move the scissors, where to steer them, the timing involved, etc. The ’pattern‘ of movement is stored in the sensory cortex and the motor cortex ‘follows’ the pattern. The motor cortex is acting as a servomechanism by following, not controlling the blueprint for movement.

Signal

Our nervous system consists of many cells (neurons) which detect and transmit signals to and from the brain. Neurons have a body with branches (cell body), attached to a long tube of cell membrane (axon) with more branches at the tail end (dendrites). Nervous signals travel from receptor cells, through the cell body and axon and out through the dendrites to the next nerve, muscle or gland. There is a small gap at the end of the dendrites, so they use chemical transmitters (hormones such as adrenaline) to maintain the nerve signal.

Nerves use electrochemical methods to send signals to the brain. Specialised nerves called receptors detect a change in the environment (such as heat). There is fluid inside and outside the nerve which contains dissolved ions (positive or negative groups of atoms). The electrochemical signal consists of potassium and sodium ions moving across the nerve’s cell membrane. This creates a wave of ‘electricity’ to move along the nerve.

Simple harmonic motion

When something moves with a simple, repeating backwards and forwards (to and fro /up and down) movement, like a pendulum, its motion is simple harmonic. Most natural vibrations are simple harmonic motion.

A marking pen attached to a pendulum in simple harmonic motion will make a straight line on a stationary piece of paper. Move the paper at constant rate at right angles to the swing of the pendulum, and the marking pen will trace out the shape of a sine wave.

In simple harmonic motion, the velocity is constantly changing due to the forces acting on the swinging object. This means that the object is always accelerating, and the acceleration changes in a predictable way.

Once the object is moved from its rest (equilibrium) position, it is always being pulled towards that rest position by a force called a restoring force. This may be provided by gravity (as in the case of a pendulum), or by buoyancy effects or elasticity in springs.

The period of the motion (the time taken to make one complete to and fro movement) in the case of a pendulum or trapeze is determined by the length of the pendulum and the value of the restoring force, in this case gravity.

It does not depend on the mass attached to it, and is affected to only a small amount by the amount of displacement from the equilibrium position.

Since the motion is regular it is predictable.

This predictability is the basis on which trapeze artists rely, it is important that the catcher is there to do the catching!

Sound

Sound is a form of energy that is produced by vibrating objects and is detected by our ears. The energy of the vibrations is transmitted as compression waves (longitudinal waves). To be transmitted, something has to be compressed, so there is no transmission (and therefore no sound) in a vacuum. (Don’t tell the science fiction movie producers though, silent battles in space just wouldn’t have the same impact.)

In a longitudinal wave, particles of the medium vibrate backwards and forwards parallel to the direction the wave is travelling. The vibration of the particles of the medium means that there are some regions where the particles are pushed close together (high pressure regions or compressions) and other regions where the particles are spread out (low pressure regions or rarefactions). Compression waves reaching the ear cause the eardrum to vibrate. Mechanisms within the ear amplify the vibrations, then convert the energy into electrical energy for transmission to the auditory region of the brain where they are interpreted.

The rate (frequency) of vibrations determines the pitch of the sound. Fast vibrations produces a high pitched sound, a high note. Frequency is measured in vibrations per second, or hertz (Hz).

Speed

A common term which simply means how fast something is travelling. The direction of travel is irrelevant. Therfore, speed is a scalar quantity. Compare this to velocity, which is how fast and in which direction something is travelling. Velocity is therefore a vector quantity.

Speed is measured in metres per second (m/s).

Standing waves

A standing wave is set up when two waves of equal amplitude and wavelength pass through each other in opposite directions. The two waves together form regions of very large amplitude (the antinodes) and regions of zero amplitude (the nodes). This is a state of resonance.

Standing waves are produced in organ pipes when vibrations are introduced at one end to produce a compression wave that travels to the end of the pipe and then is reflected back into the pipe, travelling in the opposite direction. Each organ pipe is of the correct length (and diameter) to produce a standing wave of a particular wavelength and therefore a particular note.

In a pipe that is closed at one end, the air at the closed end cannot vibrate and a node is formed at this end, an antinode at the open end. If the pipe is open at both ends, then an antinode is formed at each end.

Subitizing

Most people can instantly recognise quantities up to about seven. The recognition of a quantity without counting is known as ‘subitizing’ among psychologists.

It is very difficult instantly recognise or subitize quantities greater than seven. Instead, we guess or estimate.

However, it is possible to recognise the quantity if the pattern is seen as blocks of smaller recognisable quantities rather than a random scattering.

Tangent

A tangent to a circle is a straight line that touches the edge of the circle without passing through the edge.

Topspin

A ball in flight is said to possess topspin if the top of the ball is spinning away from you as it travels. To find out more, see ballspin.

Torque

To make something turn (or topple) there needs to be a push or a pull on the object somewhere away from the centre of turning (the pivot point). You have difficulty opening a door if you push or pull on it near the hinge, but the same amount of force near the opening edge has much more effect. A torque makes things turn — it produces rotation, and its value depends on the force applied, and the distance from pivot. It is what you use to turn on a tap or open a door. Toppling is also caused by the presence of a torque.

Torque is measured in newton metres (Nm).

Vector

A vector quantity is one which has both magnitude and direction. A quantity which needs only magnitude to describe it fully is called a scalar quantity. Speed is an example of a scalar quantity. You can describe your speed fully by saying that it is for example 20 metres per second. Velocity is the vector counterpart of speed. To fully describe your velocity you would need to say it was 20 m/s in a particular direction! Other examples of vector quantities include acceleration, force and momentum.

When vector quantities are added, the direction is very important. For example if you apply two forces to an object, the result can vary greatly depending on the direction of the forces. If both forces push in the same direction, then the object may well move in that direction. If the two forces push on the object in opposite directions, the object may just get squashed, or it may move off in the direction of one of the forces if one of the forces is much bigger than the other! Two forces pushing at an angle would cause the object to move at an angle between the two directions, and closer to the angle of push of the larger force.

To travel in a circle requires that the direction of travel constantly changes.

In cha cha, at any moment, each car has a particular velocity which is the result of the main arm velocity and the rider arm velocity together. Adding together two vectors which themselves are constantly changing over time can produce some interesting patterns.

Velocity

Velocity refers to the speed at which something is travelling AND the direction in which it is travelling, as opposed to speed, which is simply an indication of how fast something is travelling, regardless of the direction. For travelling in a straight line, the speed might be given as 20 metres per second (m/s or ms^-1), the velocity would be given as 20 metres per second northwards (assuming it was travelling in a northerly direction).

To go round a corner or travel in a circular path, the direction is constantly changing. This means that the velocity is constantly changing, and so acceleration is happening: even if the speed is constant.

Velocity is measured in meters per second (m/s).

Vertigo

This feeling is one where you feel that you or your surroundings are moving when there is no actual or very recent movement. It is the same sensation as dizziness, but in this case the feeling cannot be explained by body movements or recent movement experiences. It can be a spinning feeling, or a tilting feeling. Some people experience these feelings when looking down from a high place, when the automatic adjustments of the body to apparent motion can result in disaster! The word vertigo is sometimes used in relation to the fear of heights.

Balance is impaired as the brain directs muscles to compensate for the apparent movement. In extreme cases it can cause nausea and even vomiting. Vertigo occurs when the brain receives conflicting information from the various balance/movement sensing devices of the body.

Volume

The space occupied by a gas, liquid or solid is known as volume. It is usually measured in or millilitres, litres or cubic centimetres (cm³) and cubic metres (m³). One cm³ is equal to one millilitre (ml).

The volume of a cuboid container may be calculated by the equation

volume = height × breadth × length

V = h × l × b

Vortex

Vortex is the name given to the apparent structure formed by molecules of a fluid travelling in a spiral motion, giving a whirlpool effect. Water flowing down a plughole forms a vortex, as does a fluid travelling through a small space.

Particles within the fluid are drawn towards the exit ‘hole’, and so are pulled towards the centre and in the direction of the hole. So are many other particles: all at the same time. The initial momentum of each particle and the crowding of particles together means that many particles are ‘off centre’ as they get closer. The central pull acts as a centripetal force, producing a spiralling motion towards the point of suction. The spiralling starts in one particular direction, influenced by a number of factors, and once started, influences all the other particles in the same direction. The centripetal force is greater towards the centre so there the slope of the vortex is greater.

The angular momentum of the water stays the same as it moves towards the exit (if we ignore friction effects), so the water speed increases as it gets closer to the centre of the spiral.

It is often stated that the direction of spiralling depends on your geographical location, north or south of the equator, due to the Coriolis effect. This has been demonstrated to be false. While the Coriolis effect is real and influences the direction of spinning in tropical cyclones. there are many other dominating factors with water going down plugholes, including which way the pipe bends after the plughole. For an expanded description of the Coriolis effect and toilet bowl water, check out the web at Discovery.com

Wavelength

Sound travels through air as a longitudinal compression wave. A vibrating object causes the air to vibrate. Particles of air vibrate parallel to (along) the direction the wave is travelling; air molecules are squashed together then moved apart producing high pressure and low pressure regions. The wavelength of a sound is the distance between successive high pressure points.

Weight

Weight is a measure of the net gravitational force acting on something. What we interpret as weight here on Earth is a measure of the force due to the gravitational attraction between the Earth and the things on or near to the Earth. Gravity causes us to push on the surface of the Earth, and this push is what we call weight. If the surface of the Earth was not in the way we would accelerate towards the centre of the Earth.

Weight then can vary depending on where an object is: and also on what is happening to it. If you visit the Moon, your weight will be much less on the Moon (about one sixth). The gravitational force is affected by the mass of the two objects concerned, and the distances between the centres of the objects. The mass of the Moon is much less than Earth, reducing the gravitational force. The Moon is much smaller, so at the surface you are closer to the centre of the Moon, so increasing the gravitational force. These two together result in an overall gravitational force of about one sixth that on Earth.

Weight is measured in newtons (N).

Weightlessness

In order to understand weightlessness, it is important also to understand the difference between mass and weight. Mass is to do with how much stuff something is made of. Weight is a measure of the net gravitational force acting (zero gravity). Real weightlessness occurs when there is no net gravitational force acting on a body.

Apparent weightlessness can be experienced in a number of ways while here on earth. All you have to do is accelerate downwards at the same rate as the Earth's gravity would accelerate you due to its attractive force (ie at 9.8 metres per second per second.)

Next time you are in a lift (a fast one, when the acceleration is great), notice how you feel as the lift accelerates upwards, you feel heavier, and when the lift accelerates downwards, when you feel much lighter, as if you have been left behind, and are floating!! How you feel (weightlessness-wise) depends on the force the lift exerts upwards on you. As the lift accelerates upwards, it pushes harder on you, you push harder back on it, you feel heavier.

Work

When the action of a force causes energy to be transferred to another object or to be transformed from one form to another, then work has been done, and is equal in value to the amount of energy transferred or transformed.

In every case where work is done there is the application of a force, and the movement of something by that force. The amount of work done is given by

work = force × distance

A weightlifter holding up a 100 kg mass did work to lift the mass by applying a force to counteract the gravitational force. However, in holding the mass up, no further work is being done on the mass, because the mass is not moving! All the energy the weightlifter is using to keep the mass up is being used to contract muscles, that is where the movement is, and that is where the work is being done.

Work is measured in joules (J).

Zero gravity

See weightlessness.